Malaria is a severe disease that continues to rank among the most prevalent infections in tropical areas, throughout the world. The fact that immunization with irradiated sporozoites can protect not only rodents, but also humans against this disease indicates that it might be feasible to develop an effective pre-erythrocytic vaccine, which would represent a valuable additional tool for the control of this disease. The overall aim of this proposal is to use a replication-defective recombinant adenovirus, expressing one or more plasmodial antigens, as a model system to characterize the protective immune response targeted against the liver stages of malaria parasites. My earlier studies have demonstrated that a single immunizing dose of this vector, expressing the circumsporozoite (CS) protein, unlike any other form of presentation of this plasmodial antigen, induces high levels of CS-specific CD8+ and CD4+T cells, and confers sterile immunity to a considerable percentage of mice. I also determined that this protection is primarily mediated by CD8+ T cells, but the molecular basis of this protective mechanisms remains to be elucidated. This I propose to pursue by the use of genetically manipulated, knock-out mice. Another important issue, particularly for future vaccine development relates to the exploration of various approaches aimed at enhancing the protective effect of a subunit vaccine based on recombinant adenovirus. These objectives will be pursued by: 1)Determining the level and persistence of humoral and cell- mediated anti-plasmodial responses and protection of mice receiving multiple immunizations with recombinant adenovirus vectors, or combined immunization with other immunogens containing the CS protein. 2) Determine whether immunization with an adenoviral vector co-expressing two or more pre-erythrocytic antigens, can potentiate the immune response which occurs upon immunization with one of these antigens. Investigate the possibility of modulating this immune response by administration of an adenovirus co- expressing a plasmodial antigen and a selected lymphokine/co- stimulatory molecule, and 3) Analyze the anti-plasmodial effector mechanisms of CD8+T cells and characterization of the molecules involved in the in vivo processing and presentation of the CSCD8+ epitope.